1. Field of the Invention
The present invention relates to the field of wound dressings, and more particularly to powders which assist in wound healing.
2. Prior Art
Cornstarch has been known as a soothing and drying agent for irritated skin, such as diaper rash. Cornstarch is a dextrin, and contains amylase.
The Dressings Times, Vol. 3, No. 2, discusses wound dressings which employ sugar pastes. (http://www.smtl.co.uk/WMPRC/DressingsTimes/vol3.2.txt. It reports that, in 1976, Herszage and Montenegro of Argentina used ordinary sugar to treat the wounds of two patients with post-surgical necrotic cellulitis. Further successes followed and in 1980 they reported on the use of sugar paste in 120 infected wounds and recorded a cure rate of 99.2%.[1] The time taken for the wounds to heal varied between 9 days and 17 weeks, but it was observed that odour and secretion began to diminish within 24 hours and disappeared totally after 72 to 96 hours of treatment. In 1985, Trouillet et al[2] described the use of sugar in the treatment of 19 patients with acute mediastinitis following cardiac surgery. Wounds were packed every 3 to 4 hours with ordinary commercially available granular sugar (sucrose). The authors noted near complete debridement followed by the rapid formation of granulation tissue and eradication of bacterial infection after an average of 7.6 days of treatment.
Sugar was first used as a dressing in Northwick Park Hospital in 1982 when it was placed into infected radical vulvectomy wounds that had not responded to more conventional therapies. However, due to the nature of such wounds, packing with granular sugar was found to be impossible and therefore a thick paste was developed. Other early patients to be treated with sugar at Northwick Park were two hypo-gammaglobulinaemic individuals who had developed extensive tracking sinuses. For these, a thin paste was formulated that could be injected into the narrow wounds.
Thick sugar paste has a consistency similar to that of modeling clay and can be molded in the gloved hand immediately prior to packing into cavities with large openings such as pressure sores. Thin sugar paste resembles thin honey; it is suitable for instillation into cavities with small openings with a syringe and fine plastic tube or catheter.
Formulae for sugar pastes (Prior Art)ThinThickCaster sugar1200g1200g(fine granular sucrose)Icing sugar - additive free1800g1800g(powdered sucrose)Polyethylene glycol 4001416ml686mlHydrogen Peroxide 30%23.1ml19ml(Final concentration of hydrogen peroxide is 0.15% v/w.)
The pastes are prepared in the hospital pharmacy by combining the H202 with the PEG 400 and then incorporating this solution into the sugars with the aid of a mechanical mixer.
When homogenous the paste is packed into screw capped plastic containers and stored at 4 C. The pastes are chemically stable for at least 6 months from preparation.
Polyethylene glycol (PEG) 400 was chosen as the lubricant because it does not interact with other components of the paste and is used in a variety of pharmaceutical preparations. It is a synthetic polymer that is also used in the cosmetic industry and has significant anti-bacterial properties. [3][4] Polyethylene glycol 400 can be absorbed from mucous membranes and high blood levels may be nephrotoxic.[5] Although no toxic effects have been noted in our patients, many of whom are elderly and frail, sugar paste should be used with care in patients with impaired renal function as any absorbed polyethylene glycol is excreted renally.
Sugar paste has been used on most wound types but it has been found to be particularly effective for treating infected and malodorous wounds. Twice daily application are advised to provide the optimum antibacterial effect. This has been demonstrated both in patients with malodorous wounds (when the smell of infected necrotic tissue is removed after 2-3 days), and in patients with infected abscesses. Irrigation with thin sugar paste has achieved successful results in patients with chronic discharging sinuses who had previously failed to respond to other therapies. Repeated application over 3 to 6 weeks is generally required to bring about complete healing. Sugar paste lowers the pH of wounds to approximately 5 which may be important in infected wound although the paste does not stimulate or retard granulation tissue formation in clean wounds in the pig model.[6]
Sugar paste (thick and thin) is rapidly bactericidal against all organisms so far tested when challenged according to a modified British Pharmacopoeia antimicrobial preservatives effectiveness test. When samples of the paste were inoculated with Staphylococcus aureus, Streptococcus faecalis, Escherichia coli or Candida albicans, to give 105 cfu/gram, less than 10 cfu/gram were detectable after 1 hour at 25 C.[7] Pastes diluted with serum have a reduced bactericidal effect—75% paste in serum gave an 80% reduction in viable numbers of S. aureus within 2 hours and a 99% reduction in viable numbers of Proteus mirabilis within 1 hour[3].
Although the application of sugar to a wound creates an environment with low water activity (aw) and high osmotic pressure, overall the wound remains moist. (The water activity of a solution is the ratio of its water vapour pressure to that of pure water at the same temperature so that aw=P/Po).
The effect of reducing water activity values on the growth of bacteria has been investigated by Chirife et al[8] who determined the limiting water activities at which different species of bacteria will grow. We have determined the water activity of our pastes, at different dilutions in serum, by measuring water vapour pressure at 25 C with an electronic hygrometer. Undiluted pastes have an almost zero availability of water because the sugar (sucrose) is dispersed in Polyethylene glycol 400 which does not contain water. Sugar has an osmotic action which can be thermodynamically related to water activity by the following equation:[8]O=(RT/V)×log(1/aw),
where O is the osmotic pressure,
R is the gas constant,
T is the absolute temperature in degrees Kelvin,
V is the partial molal volume of water, and
aw is the water activity.
Thus, by determining water activity, the osmotic pressure can be calculated. From this equation it will be seen that a solution of low water activity has high osmotic pressure.
Because of the difficulty of conducting a controlled trial of sugar paste in human wounds, an animal study has been conducted[6] using a method similar to that reported by Winter and Scales.[9] Full thickness wounds 25 mm square, and 9 mm deep were made in the backs of pigs and around each was placed a colostomy stoma ring. This in turn was covered with a semipermeable plastic film dressing (Opsite) so as to form a moist chamber. Wounds were either covered with Opsite alone, or packed with thick sugar paste or cotton gauze soaked in various antiseptic solutions and then covered in Opsite. The results showed that there was no significant difference between wounds left unpacked, but covered with Opsite, and those Opsite covered wounds packed with sugar paste, indicating that although sugar paste did not stimulate the formation of granulation tissue, neither did it cause inhibition or toxicity. However, all wounds packed with antiseptics showed evidence of delayed healing, especially those containing chlorhexidine gluconate 0.2%. The pig model wounds were not infected so no conclusions can be drawn on the relative value of Opsite and sugar paste for healing infected wounds.
Dressing Times concluded that sugar paste should be considered for the management of all infected and malodorous wounds. It is a far less expensive alternative to Debrisan and similar products which are of dubious efficacy and are often difficult to remove from wounds. Sugar paste was also considered superior to charcoal dressings for treating malodorous wounds as it removes the cause of the smell and in this respect is similar to metronidazole gel. However sugar paste may be preferable to metronidazole gel for treating such wounds as the use of topical antibacterials and antibiotics should be avoided.[10]
Sugar paste lacks the toxicity of most antiseptics and it does not disrupt the architecture of the healing wounds, as does packing with gauze.
The paste is self-sterilizing and can be produced in different viscosities to suit all kinds of wound and it is not painful to apply. It may cause bleeding when granulation tissue is well formed, at which stage simple, non-impregnated dressings should be applied which will keep the wound moist and allow epithelialisation to occur.